In recent years, the biological, clinical, pharmaceutical, and other research communities have recognized that microarrays are useful, high-throughput research tools to measure a variety of biological or biochemical interactions and functions. For instance, microarrays on slides or in other formats can conserve limited or costly reagents or materials for biological or biochemical analyses. With widespread acceptance, the microarray format is likely to remain a key research tool into the foreseeable future. Applications for microarray technology will continue to expand in the areas of drug discovery and development, chemical detection, diagnostics, and basic research.
The surface chemistry and the surface morphology of the microarray substrate are important factors, which impact the quality of data derived from assays using microarray readings. In the fabrication of microarrays, the surfaces of both organic and inorganic substrates are typically modified by the deposition of a coating or a polymeric film to promote adhesion and improve immobilization or attachment of biomolecules. Substrates with poor quality surface chemistry often result in low binding efficiency, poor spot morphology, and unacceptably high residual background signal that can be non-uniform.
In the preparation of microarrays, the creation of a stable surface chemistry on inorganic substrates, such as glass slides or other silica-based surfaces, which can support a variety of biological species, is one among several important factors. For instance, the preparation of membrane protein arrays is particularly challenging because difficulties associated with preserving the correct structure-folded conformation of proteins in an immobilized state. Membrane proteins, such as G-protein coupled receptors (GPCR) maintain their folded conformations when associated with a lipid bilayer membrane. The structure and properties of lipid molecules and membrane receptor-associated lipids immobilized on a solid surface strongly depend on the chemical nature of the surface. Silanization, the application of an aminosilane to glass substrates, creates an amine-rich surface that is ideal for attaching biological membranes, membrane proteins, or proteins, as well as nucleic acid molecules (e.g., DNA or oligonucleotides) to the substrate surface.
If not handled properly during the fabrication process or, afterwards, during storage or transport, microarray substrates are susceptible to damage and degradation of the surface chemistry. Several molecular processes, may impact the functionality and quality of amine-coated surfaces. In particular, exposure to atmospheric carbon dioxide, for instance, can modify the surface chemistry and wettability characteristics of amine-coated slides.
The reactions between carbon dioxide and amines have been studied (P. V. Danckwerts, and M. M. Sharma, The Chemical Engineer, October 1966, pp. 244–280). Carbon dioxide reacts with primary or secondary amines to form carbamate or bicarbonate, respectively, in dry or humid conditions. (See, H. Y. Huang et al., “Amine-grafted MCM-48 and Silica Xerogel as Superior Sorbents for Acidic Gas Removal from Natural Gas,” Indus. Eng. Chem. Res., 47, 2427–2433 (2003)). The reaction is the following:2RNH2+CO2→RNHCOO−RNH3+  [1].It is a second-order reaction. The kinetics of the reaction is given by:
                                                        ⅆ                              [                Am                ]                                                    ⅆ              t                                =                                                    k                am                            ⁡                              [                Am                ]                                      ·                          [                              CO                2                            ]                                      ,                            [        2        ]            where [Am] represents the concentration of free amines, [CO2] the carbon dioxide concentration, kam is the rate constant and t the time. The formation of the carbamate is believed to occur in two steps, the rate-determining step is the insertion of CO2 into N—H bond which probably involves the reversible formation of a Lewis acid-base adduct followed by the very rapid protonation of another amine molecule.
Alternatively, interactions between the coated substrate surface and organic molecules can also detrimentally affect the performance and quality of the substrates. Conventional materials are inadequate to prevent such degradation of the surface chemistry. Conventional containers used to store microarray substrates are made typically from so-called commodity resins, such as high-density poly-ethylene, poly-propylene, poly-styrene, acrylonitrile butadiene styrene (ABS). In U.S. Patent Publication No. 2004-0031712 A1, incorporated herein by reference, Maxim et al. discuss the interaction of these conventional, non-specialty-engineered materials with the coated surface of a glass substrate, which changes the nature of the surface. Maxim et al. believed that containers made from these kinds of polymer materials out-gas certain components or units, such as monomers, stabilizers or binders, effect the surface of coated slides. That is, these components interfere with the performance of the substrate by changing the desired parameters or engineered specifications of the substrate surface. As a result, background fluorescence and the hydrophobic nature of the substrate surface increases, as indicated by increased contact or wetting angles.
Since surface properties can materially impact the quality and level of performance of an assay conducted using the microarray, maintaining a stable surface chemistry on amine-coated substrates is important. Hence, we recognize that a need exists for either new materials or materials having properties that will allow one to store microarray substrates without having them become degraded or damaged over time. To minimize these problems and/or protect the surface chemistry, the substrates require a sorbent, and packaging device that incorporates the sorbent material, which can removal trace amounts of CO2 as well as capture free organic components from within the packaging.